US2937128A - Electrolytic apparatus - Google Patents

Description

4 Sheets-$heet 1 Filed July 25, 1956 mdI 1N VEN TOR Bertram C. Haynes Sfuarf 5. Carlton BY May 17, 1960 B. c. RAYNES EI'AL 2,937,128

ELECTROLYTIC APPARATUS 4 Sheets-Sheet 2 Filed July 25, 1956 INVENTOR. Bertram C. Raynes Sfuarf 5. Carlton BY I. 8. ca 3 IN 5 I A A U 3 L & v om r V q May 17, 1960 B. c. RAYNES 3 ELECTROLYTIC APPARATUS Filed. July 25, 1956 4 Sheets-Sheet 3 FIG. 4

IN VEN TOR.

Berrramcifiaynes By Stuart 8. Carlton May 17, 1960 B. c. RAYNES E 2,937,128

I ELECTROLYTIC APPARATUS Filed July 25, 1956 4 Sheets-Sheet 4 FIG. 5

IN VEN TOR. Bertram C. Raynes BY Sfuarf 5. Carlton United States ate t ELECTROLYTIC APPARATUS Bertram C. Raynes, Euclid, and Stuart S. Carlton, Cleveland, Ohio, assi'gnors, by mesne assignments, to Horizons Titanium Corporation, Princeton, N..l., a corporation of New Jersey Application July 25, 1956, Serial No. 600,093 4 Claims. Cl. 204-244 This invention relates to the electrolytic preparation of metals. 'More particularly, it relates to an improved apparatus wherein the electrolysis of a fused salt bath may be accomplished to produce the desired metal as a cathode deposit.

The metals titanium, zirconium, niobium, tantalum, uranium and other metals of groups IVA, VA and VIA of the periodic table have recently come into prominence because they possess properties found 'to be extremely desirable in the construction of equipment for use in processes operating at high temperatures or at high levels of radioactivity. Considerable eliont has, therefore, been devoted to the development of means for producing the desired metals by continuous electrolytic methods ofiering advantages over the older pyrometallurgical processes.

'One object of this invention is to provide an apparatus for continuously producing said metals as cathode deposits in a fused salt electrolytic process. I

Another object of this invention is the provision of an apparatus within which the preparation of a purified electrolyte, the fused salt electrolysis by which ithe desired .metal is recovered as a cathode deposit, and the recovery of the cathode deposit in a form in which and at a temperature at which it is no longer reactive with the ordinary atmosphere, are all carried out in a manner designed to avoid the contamination of the ultimate metal product. Another object of this invention is the provision of an improved means for preparing the electrolyte for said electrolysis.

Another object of this invention is the provision of an improved means for recovering the cathode deposited metal without impairing its quality and without materially reducing the continuity of operation of the cell.

These and other objects will become more apparent from the following specification and drawingsin which:

' Figure 1 is a top view of the portion of theapparatus .beloWplanel-l of Figure 3; V I I Figure 2 is a top view of the apparatus as seen on plane of Figure 3;

Figure 3 is a side view taken on plane.3- o f Figure-2; :Figure 4 is a view taken on plane-4-4. of Figure 2; and Figure 5 is a view taken on plane 55 of Figure 1. Figure 1 shows a plan view of the general arrangement of the lower portion of the apparatus with the upper portion removed. As may be seen, the lower portion 'of the apparatus comprises a firstvessel 10 in which the electrolyte is melted and purified and from which the molten electrolyte is transferred, and a second vessel12 in which the electrolysis for recovering the desired metal is performed. The two vessels may be placed in communication with one another by means 14 comprising a conduit and associated structure. A drain. 16 is provided to empty the second vessel 12. In addition to the lower portion of the apparatus shown in Figure 1, the other portions of the apparatus include means for charging the two vessels and for recovering the cathode deposited metal, means for supporting the means for heating the vessels andfor ascertaining the temperatures of their contents, and means for control purposes.

. I 2 for maintaining a desired atmosphere in the apparatus, shown more completely in theremainingfigures. v

As shown in Figures '1 and 3, the melting andpurifying vessel 10 comprises a'base 18 on which there is supported a metallic shell 20 of steel, nickel or other suitable material of construction. 'Shell 20 may assume any convenient shape, a square, rectangle or any equilateral polygon being generally preferred for ease and simplicity of fabrication, although circular or elliptical shells or shells whose shapes are a combination of curved and straight sides may be employed in our apparatus. Within the shell 20 is a packing 22 of lampblack, carbon, or other suitable powdered or granular heat insulating material on which there is supported an inner vessel 24 prefabricated from structural elements of any suitable material of construction, such as graphite or ceramic. In a preferred embodiment, shown in the drawings, the inner vessel serves as the anode. It will, of course, be understood that a separate anode may be substituted if an electrically neutral vessel is employed. Between the inner vessel and the outer shell the packing of granular material provides a zone into which the contents of the inner vessel may leak in a controlled manner as described in a copending application Serial No. 504,952, which issued February 26, .1957, as United States Patent 2,783,195 and which was tiled jointly by one of the present applicants. Heating means 26, which maybe one or moresuitable immersion .typeheaters, is suspended in the inner vessel and serves to melt the :salt, thus forming the electrolyte. Means 27 for suspending a thermocouple in the melt may be provided I A charge hopper 28 controlled by valves 30 and 30'. permits the charging of weighed amounts of the ingredients constituting the electrolyte into the inner vessel. Hopper 28 is detachably supported on a flanged plate 29. A conduit 3-4 connects hopper 28 with a cover 32 through which it enters vessel 10. Cover 32 seals off and provides anair-tight shield for the top of the vessel 10. A connection 36 is provided to manifolds (not shown) for maintaining a vacuum or admitting argon or other-inert atmosphere into the hopper 28 and conduit 34. An ,exhaust vent is provided to vent any gases evolved during the preconditioning .of the electrolyte.

Projecting through one side wall of the first vessel 10and extending into the second vessel 12is a means which serves to pass :the salt chargepwhen molten, from the first vessel to the second vessel without exposure to the influence of a reactiveenvironment likely to contaminate the charge ofmolten salts. Thismeans, generally designated as 14, includes a conduit comprised of an impervious graphite riser 38 connected through a threaded elbow 40 to aninclined'tube 42 which passes into the'second vessel, together with inlet means 41, through a side wall of vessel 10, through which inert gas under pressure is admitted to cause the molten contents of vessel 10 to flow through riser 38 and tube 42 and into vessel 12. When it is desired to subject the contents of vessel 10 to electrolysis for the purpose of removing various impurities, a cathode (not shown) may be supported by the superstructure, e.g. by plate 29 in place of charging hopper'28.

The second vessel 12 constitutes the main electrolysis unit and is similar in many respects to the first vessel .10. It comprises a supporting shell 50, granular packing 52, an inner container 54, heaters 56 and 56', thermocouple support 57, cover 58, and charging means 60 for introducing the material to be refined into the vessel.-

66, which is preferably but not necessarily cylindrical,

separates the middle compartment into a region surrounding the cathode within the inner confines of barrier 66 and a zone defined by partitions 62 and 62, the walls of the inner container 54 and'the outer surface of barrier A means for charging solid material into vessel 12 is shown in Figures 2, 4 and '5. 'As shown, separate tubes 66. Both barrier 66 and container 54 are electrically 12 is mounted on a water-cooled flanged head 70 bolted to a flange on the shell 50. Most of the mechanical operations of the cell are performed within the confines of chamber 76 defined by sidewalls .77 and 77' and upper plate 79 and a cover 150. A fitting 75 with a connection to thefinert atmosphere and vacuum manifoldssis provided in cover 150. Fitting 75 may accommodate a sight glass, or permit the insertion and removal'of a bath sampling device. To simplify construction, the upper assembly is cathodic and is electrically insulated from the lower (anodic) portion of the cell by means of insulating bushings 72 provided on the connecting bolts 74 joining the superstructure to the lower portion of vessel 50. The cathode 64 is supported on a rod 78 which is of hollow construction to permit the temperature of the cathode to be controlled by means of fluids during depo- I I sition and during removal of the deposit. dimensions permit, several cathodes may be supported in like fashion. The lowermost portion of chamber 76, is closed by two baflles 80 to diminish the loss of heat from When the cell A the cell, or from inner container 54. The bafiles are hinged (Figure 2) at 82 and are cut away atsthe center of the vessel to provide an opening 83 for the rod 78 supporting the cathode, to permit the cathode to be inserted and withdrawn from the inner container 54. The

baffles are operated by small steel rods 84 which pass through stufiing boxes 85 to externalhandles 86.

Instead of pivoting, the baffles may be supported so as to pernnt their insertion into operating position by shding 1n grooved trackways, or in any appropriate fashion.

Means are provided within the chamber 76 to recover the cathode deposit without exposure of said deposit to any contaminating influences, particularly while it is still at an elevated temperature. As best shown in Figure 4, there is a scraper 98 ground to a knife edge and secured to the cover plate 150 on the upper assembly, to detach.

the deposit from the cathode. Other means may, how- "ever, be employed to effect the separation of the cathode deposit from the cathode. A Water-cooled receiving stack 110, to which a stufling box 112 is attached, is positioned above the chamber 76 to accommodate the heated portion of the cathode in the scraping position. To recover the deposit after it has been scraped from the cathode, there is, in the embodiment shown, a tray which is retractably mounted on a steel carriage 92 which rides on narrow steel rails 94 welded to the walls of the upper assembly chamber; a metal push rod 96 which advances and retracts tray 90 and which also rotates to permit the dumping of the deposit from tray 90, and the scraper 98. To protect the deposit from oxidation or other contaminating influence, a receiver 102, having a connection 103 to the inert gas manifold is provided. The receiver may be cooled either by the surrounding atmosphere or by a cooling coil 104 or by other means. A gate valve 105 or similar type of closure connects chamber 76 with the leading to each of the four corners of the middle compartment of vessel 12, conduct the solid material from a feed hopper 122 through a valve 126 to the portion of the middle compartment between the cylinder 66 and each of the partitions 62 and 62'. A stirrer 123 may be provided to assist in the discharge of the contents of hopper 122, and to prevent clogging of the charge material, although such means is entirely optional. Feed hopper 122 is also provided with a connection 124 to the vacuum and to the inert gas manifolds. Inlet openings 128 in cover 150 are closed by valves 130 located above the four corners of the middle compartment. Openings 128 provide access to the charge, to permit the insertion of suitable means to tamp or compact the charge; to measure the height of the materials in the vessel; to ascertain the physical condition and disposition of the charge in the vessel and to permit samples to be taken for con; trol purposes.

A salt drain 16 is provided at the bottom of vessel 12, through which the molten electrolyte may be tapped ofi at any time. Drain 16 is essentially a nickel pipe 15 lined with graphite and extending through the crucible and cell walls, and shaped or inclined so that the ,drain opening 132 is above the bottom of the inside of container 54, so that a liquid seal is formed in the drain means. As shown, pipe 15 is preferably inclined upwardly as it leaves vessel 12. The outer end of pipe 15 is water-cooled and an electrically .insulated graphite electrode extends through the center of the pipe into the salt bath. An outlet 132, leading to a removable drain pan, is provided near the outer end of the pipe. On addition of the first charge of molten electrolyte to the cell or on melting a solid charge, a small quantity of the salt enters the pipe and freezes to .form a plug in the tube. When it is desired to drain the cell a cathode lead is attached to the electrode, completing a circuit through the electrolyte to the anode. The electrode then serves as a resistance heater which quickly melts out the salt plug, permitting the contents of the cell to drain. The drain hole is sopositioned as to retain at all times a liquid seal against air entering thecell at completion of draining.

In order to prevent contamination of the molten salts or heated solid materials, it is necessary to provide an inert environment in the free spaces of the apparatus. As is customary in this art, an inert atmosphere, that is, one which does not react appreciably with the contents of the apparatus, is required. The usual atmospheres are composed of one or more of the noble gases. Such means for evacuating or flushing the several portions of the apparatus and means for maintaining any desired atmosphere therein have been previously described. Any suitable arrangement of valves and manifolds'may be -provided so that either vacuum or a noble gas such as argon orhelium maybe selectively maintained in vessel 10, vessel 12, and the charging and discharging means associated with these vessels.

Thus the vessel 10 is connected by means 41 to the inert atmosphere manifold and when it is charged from hopper 28, the desired'atmosphere is maintained by means of a connection 36 to vacuum or to the inert atmosphere manifold. Furthermore, a vent permits the removal of extraneous gases from vessel 10.

The main electrolysis vessel 12 is charged with solid materials by means of a feeder 122 provided with a connection 124 to the vacuum and to the inert gas manifolds, and is connected through manhole 1G6 and valve 105 to a connection 103 to the inert atmosphere manifold.

The entiresystem is flushedwith argonor othehnohle gas, to provide an inert atmosphere inthe system before 1 heating any of the apparatus. Vessel is then heated to any convenient temperatureabove-themeltinggpoint of the salt charge while under the inert atmosphere. The individual salts or a weighed proportioned charge of a diluentsalt such as sodium chloride (NaCl) and 'acarrier salt providinga simple or complex ion of ,the metal to "be refined is charged into the charging hopper. The hopper isv evacuated through line 36' and flushed with argon several times to remove entrainedzair. Valve 30 is opened and the salt charge is dropped into-the inner vessel, where it melts rapidly. If salts of low purity are used, it" may be found desirable to pre-electrolyae. the melt, but this step is optional. Ere-electrolysis is effected by removing the salt feeder-charge hopper 28 witli val've 30 closed. A flange in which a cathode is retractibly mounted is substituted in its stead and connected to flange 29. The top of the stack is evacuated and then flushed with argon. With the salt charge at operating tempera ture, e.g. about 900 C., the cathode is lowered into the bath, while impressing a slight polarizing voltage on the cathode. After the cathode has been lowered into the bath, the current is increased to provide a voltage'and current density just sufiicient for a small amount of free halogen gas (chlorine) to form at the anode. At the same time, oxides and water in the melt are decomposed and impurity metals in the salts are plated out onto the cathode. During this period, small amounts of argon are passed through vessel 10 in order to remove the chlorine and any other gaseous products evolved from the melt. After a sufiicient quantity of electrolyzing current has been passed, depending on the extent of purification required or desired, the electrolyzing current is reduced and the cathode is raised out of the melt. After the cathode has cooled, the cathode and the flange in which it is mounted are removed and replaced by the salt charge hopper, in preparation for the next salt charge to be processed.

While the salt melt is being prepared in vessel 10, vessel 12, filled with argon or other inert gas, is slowly heated to operating temperature of about 900 C. When both vessels are at the operating temperature, a pressure equalizer between them is closed, the vent 140 is closed and flow of the inert gas through line 41 into vessel 10 is increased. The molten salt is thereby caused to flow up riser 38 and through the inclined tube 42 into the larger vessel 12. The transfer of about 50 pounds of molten salt has been effected readily in about 30 seconds; The operation is completed, after the melt has been blown over, by closing inlet 41 and by opening the vent-140.

Since, with continuous operation, the main function of vessel 10 is to provide molten salt melts of suitable purity to vessel 12 and since the loss of salts from vessel 12 is usually only a small fraction of the total contents of vessel 12, the capacity of vessel 10 is preferably but a fraction of the capacity of vessel 12 desired for the electrolytic refining operation. While not in use, the vessel 10 may be maintained at a temperature lower than operating temperatures in order to reduce the heat-up time required for subsequent operation. Make-up salt additions may be melted and purified at any time and either blown into the cell immediately after preparation, or held molten at temperature until transferred, orcooled and held in reserve after pre-electrolysis and purification. Material to be refined, for instance small pieces or titanium scrap as described in our copending application Serial No. 596,450, filed July 9, 1956, is placed in each feeder 120 and the feeder is evacuated and flushed with argon. Baffles 80 are opened, and a steel rod is inserted in the cell through the opening 128, in the corner into which the material is to be charged. The valve 126 in corners to ahei'ght of about 2-to 4 ii1che's" belowthehei'ght I ofthe-m'elt'in'vessel 12. I

Once. the cell is in operation, Iboth' molten -salta'nd the scrap, sponge, or other material'tobe refined' ma'y be) charged without interrupting the electrolysis.

Electrolysis is effected by lowering the-cathode"into the-melt. On'initial insertion a small polarizing-voltage ismaintai-ned on the cathode to prevent the cathodefrom dissolving in' the bath. The ele'ctrolyzing current and voltage are increased to the operating level. When the cathode temperature rises above a predetermined upper level;- cooling of the cathode is initiated--and regulated to maintain an indicated internal cathodetemperature well: below the melting point'of the cathode About 10 minut's before the terminationof the run, the, cooling of thecathode is discontinued, in preparation for theremoval of the deposit. The maximum size-of deposit is determined principally by the size of perforated cylinder 66 which serves as the anode. Cathode deposits representing between 1500 and 2400 ampere hours of electrolytic current have been successfuly produced in our apparatus. With the cathode temperature increased to about 800 C., the hinged heat shields are opened and the cathode is raised to a level just below the scraper 98. Tray is moved directly under the cathode deposit by means of rod 96. The cathode is then pulled up against the knifeedge of scraper 98, to scrape the deposit onto the tray. When the deposit has been removed, cathode motion is stopped; the tray is retracted and the deposit is dumped through the gate valve into the receiver. Following this, the cathode is lowered into the bath for a repetition of the process. Raising, scraping and lowering of the cathode may be accomplished in less than 60 seconds with the apparatus shown. The cathode deposit is permitted to cool and after it has reached a temperature below that at which it reacts with the atmosphere, manhole door 106 is opened and the deposit is removed. The door is replaced and the receiver is evacuated, flushed with argon, and is then ready for another run.

From time to time additional material tobe refined is added to the corners of the middle compartment of vessel 12 to maintain it between 2 and 4 inches below the surface of the fused salt electrolyte.

It will be seen that we have provided a simple and efficient apparatus for the electrolytic refining of impure charge material, characterized by the provision of an improved means for conditioning the electrolyte and for avoiding contamination of both the intermediate and final products by oxygen or oxygen-containing compounds during the refining operation and for permitting essentially continuous electrolyses to be carried out without interruption for making additions of solid material to be refined and of makeup salts. Furthermore, the apparatus may be used to produce primary metals in which only fused salt charges are processed in the electrolyzing vessel 12, for example by conditioning salts in vessel 10 and transferring the conditioned salt to vessel 12 for electrolytic processing as described in US. Patent 2,731,402, of which one of the present inventors is a joint patentee.

We claim:

I. In an electrolytic apparatus, the combination including a first vessel provided with an airtight cover; means to charge said vessel with a salt; heating means to melt said salt form a molten electrolyte; conduit means to admit and means to maintain an inert atmosphere in said first vessel, above said charge of salt; a source of inert atmosphere, maintained under pressure; a valved connection between said source of inert atmosphere under pressure and said conduit; means to admit said inert atmosphere to said vessel; anode and cathode means positioned in said first vessel, means to impress a potential across said anode and cathode means to effect an electrolytic purification of said molten salt; a second vessel adapted to serve as themain electrolytic cell; anode and cathode means in said second vessel; a source of potential connected to impress a potential between said anode and cathode means; a conduit connecting said first vessel with said second vessel whereby purified molten salt from said first vessel may be transferred to said second vessel under the influence of the pressure of inert gas on said molten salt in said first vessel; means to recover the cathode deposited, metal from said second vessel, and means to maintain an inert atmosphere in said second vessel.

- 2. The apparatus of claim 1 including a means for draining the second vessel and said means provides a liquid seal between an outlet in said drain means and the molten contents of the second vessel.

3. The apparatus of claim 1 wherein the second vessel includes means to introduce a charge of solid material to be electrorefined into said second vessel, adjacent to the anode region.

4. The apparatus of'claim 3 -in which .the second ves-- sel serves as an anode and the region adjacent said anode for receiving a charge to be refined includes a perforated graphite member separating the cathode from the anode and defining with the anode, a charge confining zone 649,565 Ackcr May 15, 1900 1,464,862 Balke Aug. 14, 1923 1,570,212 Duhme Jan. 19, 1926 1,964,736 Le Laurin et al. July 3, 1934 2,451,492 Johnson Oct.19, 1948 2,731,402 Topinka et al. Jan. 17, 1956 2,734,856 Schultz et a1. Feb. 14, 1956 2,748,073 Mellgren May 29, 1956 2,781,304 Wilhelm et a1 Feb. 12, 1957 Benner et a1 Mar. 31, 1959

Claims (1)

1. IN AN ELECTROLYTIC APPARATUS, THE COMBINATION INCLUDING A FIRST VESSEL PROVIDED WITH AN AIRTIGHT COVER, MEANS TO CHARGE SAID VESSEL WITH A SALT, HEATING MEANS TO MELT SAID SALT FORM A MOLTEN ELECTROLYTE, CONDUIT MEANS TO ADMIT AND MEANS TO MAINTAIN AN INERT ATMOSPHERE IN SAID FIRST VESSEL, ABOVE SAID CHARGE OF SALT, A SOURCE OF INERT ATMOSPHERE, MAINTAINED UNDER PRESSURE, A VALVED CONNECTION BETWEEN SAID SOURCE OF INERT ATMOSPHERE UNDER PRESSURE AND SAID CONDUIT, MEANS TO ADMIT AND INERT ATMOSPHERE TO SAID VESSEL, ANODE AND CATHODE MEANS POSITIONED IN SAID FIRST VESSEL, MEANS TO IMPRESS A POTENTIAL ACROSS SAID ANODE AND CATHODE MEANS TO EFFECT AN ELECTROLYTIC PURIFICATION OF SAID MOLTEN SALT, A SECOND VESSEL ADAPTED TO SERVE AS THE MAIN ELECTROYLTIC CELL, ANODE AND CATHODE MEANS IN SAID SECOND VESSEL, A SOURCE OF POTENTIAL CONNECTED TO IMPRESS A POTENTIAL BETWEEN SAID ANODE AND CATHODE MEANS, A CONDUIT CONNECTING SAID FIRS VESSEL WITH SAID SECOND VESSEL WHEREBY PURIFIED MOLTEN SALT FROM SAID FIRST VESSEL MAY BE TRANSFERRED TO SAID SAID VESSEL UNDER THE INFLUENCE OF THE PRESSURE OF INERT GAS ON SAID MOLTEN SALT IN SAID FIRST VESSLE, MEANS TO RECOVER THE CATHODE DEPOSITED METAL FROM SAID SECOND VESSEL, AND MEANS TO MAINTAIN AN INERT ATMOSPHERE IN SAID SECOND VESSEL.

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